Diagnostic tape cassette

ABSTRACT

The invention concerns a diagnostic tape cassette comprising an analytical test tape, a supply spool for winding off unused test tape and a take-up spool for winding used test tape, a housing and a rotational lock for the take-up spool at least against inadvertent unwinding of test tape, wherein the rotational lock comprises one of a locking teeth arrangement, friction elements, and a catch spring and spring latch arrangement.

CLAIM OF PRIORITY

The present application is a continuation based on and claiming priorityto PCT Application No. PCT/EP2007/058649, filed Aug. 21, 2007, whichclaims the priority benefit of European Patent Application No. 06 017404.2, filed Aug. 22, 2006, each of which are hereby incorporated byreference in their entireties.

TECHNICAL FIELD OF THE INVENTION

The present application relates to a diagnostic tape cassette configuredfor blood glucose testing, comprising an analytical test tape, a supplyspool for winding off unused test tape and a take-up spool for windingused test tape, a housing for the spools and a rotational lock for thetake-up spool to guard against inadvertent unwinding of test tape.

BACKGROUND

Previously individual test strips have been used in practice for theself-diagnosis of diabetics which are photometrically analyzed afterapplying a small amount of sample in order to determine the glucosecontent in the sample (blood or tissue fluid) as accurately and reliablyas possible. In order to improve the user-friendliness it has alreadybeen suggested that a plurality of tests be provided on a test tape inthe form of a tape cassette. It should be possible to insert such tapecassettes as a disposable part into compact hand-held devices in orderto enable all required analytical steps to be carried out automaticallyand rapidly.

Designs for a reversing lock to prevent tape unwinding is generallyknown, in order to prevent unintentional winding out of used tapecontaminated with blood. One exemplary design is disclosed in U.S.Publication No. 2006/0240403. Generally, a lock is provided that allowstest tape to be wound forward whereas it should be secured againstturning back in the opposite direction of rotation. In this connectionit should be noted that diagnostic tape cassettes as consumable partsare mass-produced articles which it should be possible to manufacture assimply as possible and should operate reliably with a high degree ofuser friendliness.

On this basis the object of the invention is to further improve the testtape systems proposed in the prior art and to achieve particularadvantages for their use while being simpler to manufacture.

SUMMARY

This object and others that will be appreciated by a person of ordinaryskill in the art have been achieved according to the embodiments of thepresent invention disclosed herein. In one embodiment, the presentinvention comprises a diagnostic tape cassette for use with a bloodglucose testing device, comprising an analytical test tape, a supplyspool and a take-up spool wherein unused portions of the analytical testtape are provided on the supply spool and unwound for use and whereinused portions of the analytical test tape are wound up onto the take-upspool, a housing for the spools, and a rotational lock for the take-upspool configured to prevent inadvertent unwinding of test tape from atleast the take-up spool, wherein the rotational lock comprises one ofthree designs: (i) locking teeth disposed on opposing surfaces of thehousing and the take-up spool, the teeth being shifted by an axialmovement of the take-up spool between a mutually engaged position and arelease position, (ii) a friction element attached to a housing surfacewhich is brought into frictional engagement with a facing contactsurface of the take-up spool when the take-up spool is moved axially outof a release position, and (iii) a locking spring attached to thehousing and axially pretensioned against the take-up spool which, bymeans of at least one spring latch, meshes with free-wheel teetharranged on the front of the take-up spool to prevent against unwindingof a tape loop.

A first concept of the invention is based on the idea of implementing anautomatically switching mechanism instead of a lock controlled by thedirection of rotation. Accordingly it is proposed that in one embodimentthe rotational lock has locking teeth disposed on opposing faces of boththe housing and the take-up spool, said teeth being shifted by an axialmovement of the take-up spool in its spool axis between a mutuallyengaged position and a release position. In this manner it is possibleto apply or override a locking action as the situation demands. In theengaged position used test tape is reliably prevented from becomingfreely accessible by manipulation of the user. In the release positiondistracting noises are completely avoided and no additional drive torqueis required which is also advantageous with regard to energy supply whenit is used in hand-held devices. Furthermore, the proposed solutionworks independently of the coil diameter of the wound test tape and therotational lock can be manufactured using a few components withoutcomplicated free-wheel mechanisms. At the same time the overall size canbe kept small so that the functional parts are not important fordetermining the cassette size.

The locking teeth in one embodiment are in the engaged position when thetape cassette is handled independently of the testing device and are inthe release position when the tape cassette is inserted into the testingdevice, such as by inserting a drive spindle of the device into thetake-up spool.

The axial movement of the locking teeth also enables the take-up spoolto be freely rotated in both directions of rotation in the releaseposition and locks the take-up spool in both directions of rotation inthe engaged position.

In one embodiment for the construction of the tape cassette, the take-upspool comprises a collar and a cylindrical spool body around which theused portions of the test tape can be wound, the collar comprising adisk having a plurality of teeth as the locking teeth.

In order to achieve an automatic shift function, in one aspect thetake-up spool is braced against the housing in the direction of thespool axis by means of a return spring. In this connection, the returnspring is typically formed on a wall of the housing as a leaf spring orspiral spring and when an annular space is kept free for the test tapebetween the wall and the locking teeth.

The housing in other aspects has a toothed ring flange as locking teeth.

In order to avoid an unintentional locking action during axial tiltingdue to high tape tension, in other embodiments the locking teeth of thehousing are formed on a ring segment facing away from a last deflectingpoint for the test tape to be wound on and when the remaining ringsegment has no teeth.

An improved form fit in the locking direction can be achieved by meansof the fact that the teeth of the locking teeth have asymmetric toothflanks where the tooth flanks which strike one another in the engagedposition when backing the take-up spool, are steeper.

For an easy manufacture, in yet other embodiments the take-up spool isinserted into a chamber of the housing that is free of a physical axisof rotation. The assembly can also be simplified if the take-up spoolcan be placed on the locking teeth of the housing in any rotationalposition.

In order to compensate for tolerances, such as in the case of aseparately mounted rotary drive, in yet other embodiments the take-upspool is float-mounted in the housing with transverse play with regardto its spool axis. In this case it should be ensured that the transverseplay is greater than about 0.2 mm, typically between about 0.3 and about0.6 mm. In one aspect, the take-up spool has an annular extension whichengages in an opening in the housing with transverse play at least inthe engaged position of the locking teeth.

According to a second inventive concept the rotational lock comprises afriction element attached to a housing surface which is brought intofrictional engagement with a facing contact surface of the take-up spoolwhen the take-up spool is moved axially out of a release position. As aresult a locking function can be achieved in a constructionally simplemanner in any position of rotation and independently of the direction ofrotation.

The friction element in one embodiment can be formed by a friction ringarranged coaxially with respect to the take-up spool, can comprise anelastomer material, such as TPE, and can be formed on the housingsurface by injection-molding.

Another improvement is achieved in embodiments in which the housingsurface is formed by a ring flange defining an opening and in which thefriction element is arranged circumferentially on the ring flange, suchas in the area of the rim of the opening. Correspondingly, the contactsurface can then be formed by a collar of a cylindrical spool bodyaround which the test tape can be wound. The frictional force istherefore independent of the current diameter of the tape spool on thespool body.

In order to automatically ensure a frictional engagement when thecassette is not in use, in one embodiment the take-up spool is bracedagainst the housing in the direction of the spool axis by means of areturn spring such that the frictional engagement occurs under therestoring force of the return spring.

Another inventive concept is that the rotational lock has a lockingspring attached to the housing and axially pretensioned against thetake-up spool, which permanently meshes with free-wheel teeth arrangedon the front of the take-up spool to prevent unwinding of a tape loop.This not only increases protection against manipulation but can alsoalways prevent an unintentional unwinding of a tape loop for example dueto jolting and thus maintain a defined tape positioning at a sensorsite.

The locking spring in one embodiment is formed on a wall of the housing,such as in a concentric ring structure or spiral spring where an innermember of the locking spring projecting from the wall carries the atleast one latch.

In order to minimize the possible angle of backward movement with agiven number of teeth, in one aspect the spring latch is designed as amultiple latch to subdivide the locked positions of the free-wheel teethsuch that the individual latches are brought into a locking engagementwhich is displaced over the tooth pitch of the free-wheel teeth.

According to other aspects of this concept, the free-wheel teeth areformed on an end wall of a spool body of the take-up spool which facesthe catch spring, and the spool body is supported on the housing bymeans of an annular collar and possibly also by locking teeth.

In order to achieve a locking action which is dependent on the directionof rotation, in other aspects the free-wheel teeth are formed by a crowngear with an asymmetric tooth profile where the flatter tooth flanksform a slide slope for the spring latch during rotation in the windingdirection and the steeper tooth flanks support the spring latch in aform-fitting manner during rotation in the unwinding direction.

In order to minimize friction, in yet other aspects the teeth of thefree-wheel teeth have a tooth height which decreases over their widththus shortening the engagement length of the spring latch.

The invention also concerns a test system comprising a test device and adiagnostic tape cassette inserted therein for blood glucose testingwhere the tape cassette has an analytical test tape, a supply spool forwinding off unused test tape and a take-up spool for winding used testtape, a housing for the spools and a rotational lock for the take-upspool at least against inadvertent unwinding of test tape.

In one embodiment of such a system, a drive spindle of the test deviceengages in the take-up spool when the tape cassette is inserted andthereby lifts out the locking teeth or abolishes the frictionalconnection of the friction element into the release position.

Another improvement can be achieved in that the drive spindle can beadjusted by a spring in the direction of a drive axis and engages in thetake-up spool under spring displacement. In this connection, the drivespindle in a driver bore of the take-up spool transfers a rotarymovement by means of at least one driver.

The invention is to be explained in more detail by the following figuresand examples.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of the embodiments of the presentinvention can be best understood when read in conjunction with thefollowing drawings, where like structure is indicated with likereference numerals and in which:

FIG. 1 shows a tape cassette for blood glucose testing comprising anunwinding lock for the test tape in a perspective view.

FIG. 2 shows a take-up spool of the tape cassette of FIG. 1 with lockingteeth in an enlarged perspective view.

FIG. 3 shows a ring flange of the tape cassette with a counter-toothingin a top-view.

FIGS. 4 and 5 show the take-up spool of the tape cassette and the ringflange of the housing in an engaged position (FIG. 4) and a releasedposition (FIG. 5) of the locking teeth in an axial section.

FIG. 6 shows a portable measuring device with a receptacle for the tapecassette in a perspective view.

FIG. 7 shows a drive spindle of the device according to FIG. 6 in a sideview.

FIG. 8 shows the housing cover with a locking spring that is formedthereon in a further embodiment of the tape cassette.

FIG. 9 shows a take-up spool provided with free wheel teeth on the frontside in a side view.

FIG. 10 shows the locking spring according to FIG. 8 engaged with thefree wheel teeth according to FIG. 9 for a permanent loop lock in abroken perspective view.

FIGS. 11 to 13 show a further embodiment of the tape cassette with atake-up spool according to FIG. 11 for a frictional engagement with africtional ring on the housing according to FIG. 12 or 13 in aperspective view.

In order that the present invention may be more readily understood,reference is made to the following detailed descriptions and examples,which are intended to illustrate the present invention, but not limitthe scope thereof.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

The following descriptions of the embodiments are merely exemplary innature and are in no way intended to limit the present invention or itsapplication or uses.

The tape cassette shown in FIG. 1 with the cover removed enables aplurality of glucose analyses to be carried out locally on blood samplescollected by the patients themselves. For this purpose the tape cassette10 comprises an analytical test tape 12 which can be pulled from asupply spool 14 and wound onto a take-up spool 16, during which a testfield 18 is deflected at an application tip 20 in order to allow bodyfluid (e.g., blood or tissue fluid) to be applied to the front side anda reflectometric measurement to be carried out on the rear side. Thetest fields 18 mounted on sections of the test tape 12 contain drychemicals which respond to the analyte (glucose) in the applied bodyfluid and lead to a measurable change in the light radiated back whenthe rear side is illuminated.

The spools 14, 16 carrying the test tape 12 are inserted into a housing22 of the cassette 10 in which housing only the application tip 20 isfreely accessible when the cover is fitted. In order to prevent usedtest tape contaminated with blood from being unintentionally wound offduring manipulations from outside, a rotational lock 24 is providedbetween the take-up spool 16 and housing 22. In the embodiment shown inFIG. 1, this lock is formed by locking teeth 26, 28 formed on respectivesurfaces of the housing 22 and the take-up spool 16. The take-up spool16 can be shifted by an axial movement of the take-up spool along thespool axis 30 between a mutually engaged position and a releaseposition.

In the embodiment shown in FIG. 2, the take-up spool 16 has a tootheddisk 32 with teeth on the front side which carries the locking teeth 28in the fashion of a crown wheel. The toothed disk 32 is formed by acollar of a hollow-cylindrical spool body 34 around which the test tape12 can be wound where the locking teeth 28 face away from the spool oftest tape 36 (FIG. 1). The take-up spool 16 has an annular extension 38on the toothed side for a floating centring in the counter-toothing 26.

As shown in FIG. 3, the housing 22 has a ring flange 40 which carriesthe locking teeth 26 on the housing side. Said teeth are formed on aring segment 45 which faces away from the deflecting point 42 for thetest tape 12 to be wound on which is last with regard to the tapetransport direction whereas the remaining ring segment 46 has no teethso that when it is tilted due to a strong tape tensile load of thetake-up spool 16, unintentional locking is avoided. The ring flange 40defines a housing opening 48 in which the annular extension 38 of thetake-up spool 16 is pivoted in an engaged position with transverse play49. This transverse play 49 is achieved by means of the fact that thecircumference of the housing opening 48 has an approximately 0.5 mmlarger diameter than the annular extension 38. Due to their radialextension the locking teeth 26, 28 can compensate for a correspondinglateral deflection of the take-up spool 16 which can thus compensate forpositioning tolerances.

The locking teeth 26, 28 are thus formed in a ring shape on facingsurfaces 44, 50 so that the take-up spool 16 can be placed in anyrotational position on the ring flange 40. In order to improve thelocking action against a reversal of rotation, the teeth of the lockingteeth 26, 28 have asymmetric tooth flanks where the tooth flanks 52, 54that strike each other in the engaged position when the take-up spool 16is rotated backwards are steeper than the opposing tooth flanks 52, 54.

The shifting function of the rotational lock 24 is shown best in FIGS. 4and 5. When the tape cassette 10 is stored or is handled independentlyof the device, the locking teeth 26, 28 are mutually engaged so thatboth directions of rotation are locked by form fitting (FIG. 4). This isensured by a return spring 56 which is clamped between the cover 58 ofthe housing 22 and the closed front face 60 of the spool body 34 andpresses this against the ring flange 40. The return spring 56 isexpediently formed on the cover 58 as a spiral spring. The take-up spool16 can then be inserted into the housing chamber 62 where no physicalpivot axle is required and the annular space 64 between the cover 58 andthe rotational lock 24 is kept free in order to receive the test tape12.

When the tape cassette 10 is used, in one embodiment a drive spindle 66of an instrument drive which is only shown schematically in FIG. 5engages axially in the central driver bore 67 of the spool body 34 andthus under compression of the spring 56, results in it being lifted outinto the release position. In this process the locking teeth 26, 28 aredisengaged and the take-up spool 16 can thus be freely rotated. Thedrive spindle 66 then optionally adopts the locking function in theunwinding direction whereas the winding on of the test tape—in theexample shown when rotated in a clockwise direction—is made possible bythree drivers 68 divided in the direction of rotation. Due to the gapbetween the locking teeth 26, 28 distracting noises are thus avoided andno undesired braking torque occurs.

FIG. 6 shows a hand-held device 70 with a receptacle 72 into which thetape cassette 10 can be inserted in order to enable a substantiallyautomated measuring process with the measuring system that is formed inthis manner. The optical measuring system of the instrument 76 ispositioned relative to the application tip 20 in the receptacle 72. Inthis connection the transverse play of the take-up spool 16 explainedabove allows a compensation of assembly and positioning tolerances ofthe drive spindle 66 specially mounted in the device housing.

An embodiment of the drive spindle 66 shown separately in FIG. 7 has adriving pin 78 which penetrates the bottom of the receptacle 72 and iscoupled via a gearing to a drive motor in the device 70 (not shown). Asupporting disk 80 is seated on the pin 78 on which disk a coupling head82 is supported by means of a helical compression spring 84 allowingaxial movement relative to the pin 78. When the cassette 10 is insertedinto the receptacle 72, the coupling head 82 plunges into the driverbore 67 of the take-up spool 16 and its circumferential cams 86 comeinto a form-fit with the drivers 68 under the force of the spring 84 sothat a torque can be transferred.

In the embodiments of a rotational lock 24 described in the followingdescription, reference numerals common to other embodiment denote thesame or similar structure. The example according to FIGS. 8 to 10differs essentially in that a locking spring 56′ is provided on thehousing cover 58 in combination with free-wheel teeth on the take-upspool 16 to permanently secure it against unintentional tape unwinding.As a result the unwinding of a tape loop is avoided in any state of use.

In the embodiment shown in FIG. 8, the locking spring 56′ is punched outof the housing sheet 88 as a ring structure in which two coaxial rings90 are connected together by bridges. Two ring segments 92 are formed onthe inner ring and each has an end bent in each case towards the insideof the housing to form a latch 94 whereas the other piece of the segmentis held in a plastic injection-molded encapsulation covering the rearside of the spring 56′. The ring segments 92 and the rings 90 areaxially displaced relative to one another such that they form anoutwardly curved compression spring arrangement against the front face60 of the inserted take-up spool 16 (cf. FIG. 10).

FIG. 9 shows an appropriately adapted take-up spool 16 which in contrastto the design of FIG. 2, is provided on its front side with free-wheelteeth 96. This is formed by a crown gear with an asymmetric toothprofile where the flatter tooth flanks 98 form a slide slope for thespring latch 94 when it is rotated in the winding direction and thesteeper tooth flanks 100 lock the spring latch 94 in a form-fittingmanner when rotated in the unwinding direction.

FIG. 10 illustrates the action of the spring engagement which isdependent on the direction of rotation. When the take-up spool 16 isinserted, the latches 94 that are bent downwards mesh under springpretension such that in the position shown one latch butts against asteep tooth flank 100 whereas the other latch rests centrally on a flattooth flank 98. In this manner the effective tooth pitch is halved suchthat a low angle of backward movement is nevertheless achieved until thelocking action occurs with a continued and stable interlocking. In orderto reduce friction, the teeth of the annular free wheel teeth 96 canhave a tooth height which decreases over their width which shortens theengagement length of the spring latches 94.

In order to obtain an additional locking action in both directions ofrotation when it is not in use, the collar 102 of the spool body 34 canbe provided on its supporting side with circumferential locking teeth 28which engage in counter-teeth 26 on the housing flange 40. Thisrotational lock 24 is released by the drive spindle 66 during insertioninto the device 70 whereas the directionally-dependent locking action ofthe rotational lock 94, 96 is retained under higher spring pretensionbut at a lower engagement angle of the spring latches.

In the embodiment of a rotational lock 24 shown in FIGS. 11 to 13, afriction lock that is independent of the position of rotation anddirection of rotation is provided instead of the locking teeth 26, 28.According to FIG. 11, only the collar 102 of the take-up spool 16remains in this case free of gear teeth. A frictional ring 104 is formedon the support surface of the ring flange 40 of the housing 22 for thefrictional lock which either sits in the middle of the ring area (FIG.12) or at the side of the edge defining the flange opening 48 (FIG. 13).The frictional ring 104 consists of a thermoplastic elastomer material(TPE) which is injection-molded in the same manufacturing step togetherwith sealing components on the housing 22 in an injection-moldingprocess. Also in this case the frictional lock is supported by a returnspring 56 according to FIG. 4 formed on the housing 22 whereas when thedrive spindle 66 engages according to FIG. 5 the take-up spool 16 islifted against the force of the spring and thus the frictionalconnection is released.

The features disclosed in the above description, the claims and thedrawings may be important both individually and in any combination withone another for implementing the invention in its various embodiments.

It is noted that terms like “preferably”, “commonly”, and “typically”are not utilized herein to limit the scope of the claimed invention orto imply that certain features are critical, essential, or evenimportant to the structure or function of the claimed invention. Rather,these terms are merely intended to highlight alternative or additionalfeatures that may or may not be utilized in a particular embodiment ofthe present invention.

For the purposes of describing and defining the present invention it isnoted that the term “substantially” is utilized herein to represent theinherent degree of uncertainty that may be attributed to anyquantitative comparison, value, measurement, or other representation.The term “substantially” is also utilized herein to represent the degreeby which a quantitative representation may vary from a stated referencewithout resulting in a change in the basic function of the subjectmatter at issue.

Having described the present invention in detail and by reference tospecific embodiments thereof, it will be apparent that modification andvariations are possible without departing from the scope of the presentinvention defined in the appended claims. More specifically, althoughsome aspects of the present invention are identified herein as preferredor particularly advantageous, it is contemplated that the presentinvention is not necessarily limited to these preferred aspects of thepresent invention.

What is claimed is:
 1. A diagnostic tape cassette for use with a bloodglucose testing device, comprising: an analytical test tape, a supplyspool and a take-up spool wherein unused portions of the analytical testtape are provided on the supply spool and unwound for use and whereinused portions of the analytical test tape are wound up onto the take-upspool which rotates around a spool axis, a housing for the spools, thetake-up spool comprising a first face and the housing comprising asecond face opposing the first face, and a rotational lock for thetake-up spool configured to prevent inadvertent unwinding of test tapefrom at least the take-up spool, wherein the rotational lock compriseslocking teeth disposed on each of the first and second faces, said teethbeing shifted by an axial movement of the take-up spool along the spoolaxis between a mutually engaged position where the locking teeth of thetake-up spool engage the locking teeth of the housing and a releaseposition where the locking teeth of the take-up spool are axially spacedfrom the locking teeth of the housing.
 2. The tape cassette according toclaim 1, wherein the take-up spool is biased so that the locking teethare in the engaged position.
 3. The tape cassette according to claim 1,wherein the locking teeth can be moved from the mutually engagedposition into the release position upon insertion of a drive spindleinto the take-up spool.
 4. The tape cassette according to claim 1,wherein the take-up spool can be rotated in both directions of rotationwhen the locking teeth are in the release position and wherein bothdirections of rotation of the take-up spool are locked when the lockingteeth are in the engaged position.
 5. The tape cassette according toclaim 1, wherein the first face of the take-up spool comprises a disk,the locking teeth comprising teeth formed on the disk.
 6. The tapecassette according to claim 5, wherein the take-up spool comprises acollar and a cylindrical spool body around which the used portions ofthe test tape can be wound, the collar comprising the disk, wherein thelocking teeth on the disk face generally away from the cylindrical spoolbody.
 7. The tape cassette according to claim 1, wherein the take-upspool is braced against the housing in the direction of the spool axisby a return spring.
 8. The tape cassette according to claim 7, whereinthe return spring comprises a leaf spring or spiral spring provided on awall of the housing and wherein an annular space is kept generallyvacant for receiving the unused portions of the test tape about thetake-up spool between the wall and the locking teeth.
 9. The tapecassette according to claim 1, wherein the second face of the housingcomprises a ring flange, the locking teeth comprising teeth formed onsaid flange.
 10. The tape cassette according to claim 1, wherein thelocking teeth on the second face of the housing are formed on a portionof a ring segment facing away from a last deflecting point for the testtape to be wound on, and wherein a remaining portion of the ring segmenthas no teeth.
 11. The tape cassette according to claim 1, wherein thelocking teeth comprise teeth having asymmetric tooth flanks, wherein thetooth flanks which strike one another when the locking teeth are in theengaged position are steeper when rewinding the take-up spool.
 12. Thetape cassette according to claim 1, wherein the take-up spool is locatedin a chamber of the housing that is free of a physical axis of rotation.13. The tape cassette according to claim 1, wherein the take-up spoolcan be placed on the locking teeth of the housing in any rotationalposition.
 14. The tape cassette according to claim 1, wherein thetake-up spool is float-mounted in the housing with transverse playrelative to its spool axis.
 15. The tape cassette according to claim 14,wherein the transverse play is between about 0.2 mm and about 0.6 mm.16. The tape cassette according to claim 1, wherein the take-up spoolhas an annular extension which engages in an opening in the housing withtransverse play at least in the engaged position of the locking teeth.17. A diagnostic tape cassette for use with a blood glucose testingdevice, comprising: an analytical test tape, a supply spool and atake-up spool wherein unused portions of the analytical test tape areprovided on the supply spool and unwound for use and wherein usedportions of the analytical test tape are wound up onto the take-up spoolthat rotates around a spool axis, a housing for the spools and arotational lock for the take-up spool, wherein the rotational lockcomprises a locking spring attached to the housing and axiallypretensioned against the take-up spool along the spool axis, and thelocking spring includes at least one spring latch that meshes withfree-wheel teeth arranged on the front of the take-up spool to preventagainst unwinding of a tape loop.
 18. The tape cassette according toclaim 17, wherein the locking spring is formed on a wall of the housingas a concentric ring structure or spiral spring where an inner member ofthe locking spring projecting from the wall carries the at least onespring latch.
 19. The tape cassette according to claim 17, wherein theat least one spring latch is designed as a multiple latch to subdividethe locked positions of the free-wheel teeth such that the individuallatches are brought into a locking engagement which is displaced overthe tooth pitch of the free-wheel teeth.
 20. The tape cassette accordingto claim 17, wherein the free-wheel teeth are formed on an end wall of aspool body of the take-up spool which faces the locking spring, andwherein the spool body is supported on the housing by an annular collarand by locking teeth.
 21. The tape cassette according to claim 17,wherein the free-wheel teeth are formed by a crown gear with anasymmetric tooth profile where the flatter tooth flanks form a slideslope for the at least one spring latch during rotation in the windingdirection and the steeper tooth flanks block the at least one springlatch in a form-fitting manner during rotation in the unwindingdirection.
 22. The tape cassette according to claim 17, wherein theteeth of the free-wheel teeth have a tooth height which decreases overtheir width thus shortening the engagement length of the at least onespring latch.